1. Field of the Invention
The present invention relates generally to styrene insoluble fibrous mats and to a method of preparing said mats. More particularly, the invention relates to fibrous mats comprising a fibrous material and a binder resin, said resin comprising
A. a first alpha-beta ethylenically unsaturated monomer selected from the group consisting of styrene, lower alkyl acrylates, lower alkyl methacrylates, lower alkyl itaconates, lower alkyl maleates, lower alkyl fumarates, vinyl esters, and vinyl chloride; PA1 B. a second alpha-beta ethylenically unsaturated monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, acrylamide, lower alkyl acrylamides, N-alkoxy modified acrylamides, diacetone acrylamide, maleamic acid, maleamide, furamide, N-monoalkyl/aryl substituted amides, hydroxyethyl acrylate, and hydroxypropyl methacrylate; and PA1 C. a modifier selected from the group consisting of epoxy resins, melamine formaldehyde resins, and urea formaldehyde resins. PA1 a. a first alpha-beta ethylenically unsaturated monomer, sometimes referred to hereinafter as the main monomer; PA1 b. a second alpha-beta ethylenically unsaturated monomer, sometimes referred to hereinafter as the reactive monomer; and PA1 c. a modifier.
The mats are prepared by combining the fibrous material and binder resin and heating at a mat temperature of at least about 150.degree.C. for a time sufficient to cure the resin to an insoluble state.
2. Description of the Prior Art
Fiber reinforced plastics, such as glass reinforced materials, are well known in the art. These materials are generally prepared by combining fibers in the form of a continuous layer or mat with a suitable resinous composition. The resinous compositions most frequently employed comprise a polyester resin and a vinyl monomer. Of the numerous vinyl monomers which may be employed in the resinous compositions, styrene is most generally used because of its availability and low cost.
Fibrous mats for use in producing these reinforced materials are also known and can be produced in any one of several ways. In the production of said mats, it is important that the fibers therein be bonded to one another at points of contact by a relatively flexible binder, so that such a mat can be handled and fitted to the contours of a mold in which a fiber reinforced plastic is to be produced without substantial disruption of the mat. Accordingly, a mat binder must be capable of adhering glass fibers to one another and must be sufficiently flexible so that the mat can be handled and shaped as required prior to the time that a reinforced plastic is produced therefrom.
After a glass fiber mat has been packed into a suitable mold, a suitable, curable resinous composition is then associated therewith in the mold; and the molding operation, which may involve heat and pressure, is carried out. The molding operation may be matched die compression molding, hand lay-up molding, vacuum bag molding, or another process known to those skilled in the art. To be suitable for use in this part of the operation, the mat binder must be compatible with the resinous composition and, preferably, be copolymerizable therewith.
Mat binder resins which have relatively fast solubility rates in the vinyl monomers employed in the resinous compositions utilized in the preparation of said reinforced plastics are used principally in the preparation of mats which are utilized in low pressure molding operations. In the low pressure operations, there is only a slight tendency for the bonded fibrous material to be displaced and it is, therefore, permissible for the binder resin to dissolve fairly rapidly in the vinyl monomer component of the resinous composition since it is not necessary for the binder resin to maintain the bonded fibers in a set position for a prolonged period of time.
However, in high pressure operations, there is a greater tendency for the bonded fibrous material to become displaced resulting in a product in which the fibers are unevenly distributed. This is undesirable for a variety of reasons and it is, therefore, essential that the binder resin employed in a mat which is to be used in this type of operation be capable of holding the fibrous material firmly in place. To do this, the mat binder resin must have a relatively slow solubility rate in the vinyl monomer component of the resinous composition.
Previously, the classification of a bonded mat as either of the soluble or insoluble type was determined by the nature of the resin employed in the preparation of said mat. Thus, it was possible to produce a mat having the desired solubility properties by carefully selecting the binder resin employed in said mat. See, in this regard, U.S. Pat. No. 3,340,136 issued to Burns et al.
However, it would be desirable to be able to utilize a single binder resin in the preparation of either soluble or insoluble fibrous mats. In accordance with the present invention, it has been found that certain resins, as hereinafter defined, may be utilized in the preparation of insoluble mats by carefully controlling the conditions under which said mats are cured. Operating outside these conditions, the same resins are useful in the preparation of soluble fibrous mats.